Formula: Cu4(SO4)(OH)6 sulphate with hydroxyl
Specific gravity: 3.97
Hardness: 3½ to 4
Streak: Green to light green
Colour: Emerald green
Solubility: Moderately soluble in hydrochloric, sulphuric and nitric acid
Brochantite occurs as a secondary mineral in the oxidation zone of
high temperature copper ores in acid conditions. When the carbonate concentration
is similar to the atmospheric value, at successively higher values of pH (less acid conditions),
chalcanthite is replaced by antlerite
then brochantite then malachite. Although the environment for brochantite
is at a higher pH than chalcanthite and
antlerite, it is still on the acid side of neutral. In the UK brochantite is
relatively common in low carbonate environments such as the Caldbeck Fells, but much less so in the more carbonate-rich
(JRS 18.12, 13).
At Jazkazgan, Karaganda Oblast, Kazakhstan, brochantite pseudomorphs after bornite have been found (KL p191).
Primary chalcopyrite readily alters to the secondary minerals bornite, covellite and brochantite.
antlerite and water to brochantite and sulphuric acid
4Cu3SO4(OH)4(s) + 2H2O(l) → 3Cu4SO4(OH)6(s) + H2SO4(aq)
(JRS 18.12, 13)
The Activity-pH diagram below was calculated at 298.2 K for some arsenates and sulphates for constant activity (roughly equivalent to concentration) of H2AsO4- in solution, over a range of values of pH and of SO42- activity (MM 52.689).
The mineral formulae are:
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